Subspecies and the AOU Checklist Committee

Subspecies should represent geographically discrete breeding populations that are diagnosable from other populations on the basis of plumage and/or measurements, but are not yet reproductively isolated. Varying levels of diagnosability have been proposed for subspecies, typically ranging from at least 75% to 95%. Because subspecies represent relatively young points along an evolutionary time scale, genetic differentiation between subspecies may not necessarily parallel phenotypic divergence. Thus, subspecies that are phenotypically but not genetically distinct still warrant recognition if individuals can be assigned to a subspecies with a high degree of certainty. Described subspecies that represent points along a phenotypic continuum (cline) probably would not warrant recognition given further study.

One of the missions of the AOU Check-list Committee is to produce a revised Check-list that describes geographic variation and subspecies of North American birds. In order to accomplish this goal, a subcommittee has been established that will focus on this taxonomic unit. The structure and operating procedures of this subcommittee are being developed. The Committee currently is discussing ways in which this effort can be joined with that of the Birds of North America Online.